When backdoor keys are written to the flash, the block selected by the
keys remains selected and the last key is stored in the associated
data register. If a flash command is launched on a different block
before writing 1 to either PVIOL or ACCERR bits, the command
will also execute on the block where the last key was written to.
Also, commands that use the data field, such as data compress and
program commands, will be impacted by the data from the last key
written as follows:
Data compress command will compress a given number of words from
both blocks; this number will be equal to the last key written, and
the signature from the block containing the backdoor keys will affect
the signature returned in the FDATA register.
Program command will program both blocks at the same relative
address with the unselected block being programmed with a data value
equal to the last key written.